That, at least, is the tale that University at Buffalo geologist
Tracy Gregg heard from a tour guide and local hiker when she
visited the site on two occasions.

But Gregg and a colleague have a new explanation for the
presence of the lava formations — this one also
unexpected.

In the Journal
of Volcanology and Geothermal Research, she and former UB
master’s student Kenneth Christle report that the pillars,
hollow and made from basalt, likely formed in a surprising reaction
where lava met water without any explosion occurring.

Their findings appeared online Aug. 15 and will be published in
a forthcoming print edition of the journal.

“Usually, when lava and water meet in aerial environments,
the water instantly flashes to steam,” said Gregg, a UB
associate professor of geology. “That’s a volume
increase of eight times — boom.”

“Formations like the ones we see in Iceland are common in
the ocean under two miles of water, where there’s so much
pressure that there’s no explosion,” she said.
“They’ve never been described on land before, and
it’s important because it tells us that water and lava can
come together on land and not explode. This has implications for
the way we view volcanic risk.”

Deep-sea basalt pillars form when columns of super-heated water
rise between pillows of lava on the ocean floor, cooling the molten
rock into hollow, pipe-like minarets. The structures grow taller as
lava levels rise, and remain standing even after volcanic eruptions
end and lava levels fall again.

Gregg and Christle propose that the same phenomenon sculpted the
land-based lava pillars in Iceland.

It happened in the 1780s, when lava from a nearby eruption
entered the Skaelingar valley, which Gregg theorizes was covered by
a pond or was super-swampy.

She thinks one reason no explosion occurred was because the lava
was moving so slowly — centimeters per second — that it
was able to react with the water in a “kinder, gentler”
manner.

“If you’re driving your car at 5 miles per hour and
you hit a stop sign, it’s a lot different than if you hit
that same stop sign at 40 miles an hour,” she said.
“There’s a lot more energy that will be
released.”

The Iceland formations, some over 2 meters tall, display
telltale features that hint at how they were created. For
example:

They are hollow on the inside.

Their rocky exteriors bear vertical scars — scratches
where pieces of floating crust may have rammed into the pillars and
scraped the surface as lava levels in the valley declined.

The skin of the towers isn’t smooth, but gnarled with
shiny drips of rock. The glassy texture suggests that the lava
hardened quickly into rock, at a pace consistent with non-explosive
water-lava interactions. Had the lava cooled more slowly in air, it
would have formed crystals.

Each of these distinctive characteristics is also prevalent in
deep-ocean pillars, said Gregg, who first saw the Icelandic
formations in the mid-1990s while hiking in the valley with her
husband.

“I knew as soon as I saw them what they were,” she
said. “I had, at that time, been on submarine cruises and
seen these things deep under the sea, so I was just hysterical,
saying, ‘Look at these!’ So I ran around and started
taking pictures until the light started running out.”

She didn’t have the chance to return to the site until
2010, when Christle received a student research grant from the
Geological Society of America to do field work in Iceland.

The two spent four days studying the pillars in detail,
confirming Gregg’s original suspicions.

In the future, scientists could hunt for land-based lava pillars
near oceans to learn about the height of ancient seas, or search
for such formations on Mars and other planets to determine where
water once existed.

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